1. Field of the Invention
This invention relates to a tire-slip preventing device and more particularly to a tire-slip preventing device for preventing the tires of a car from slipping on an icy, snowy or muddy road.
2. Description of the Prior Art
There has recently been proposed a tire-slip preventing device of the type shown in FIG. 1 which comprises two opposite and parallel cords 1a and 1b and a plurality of cross belts 2 molded of synthetic resin or some other tough but easily deformable material. In this conventional device, the cross belts are fixed to the cords at either end by rivets or some other fastening means so that when the device is laid out it has the form of a ladder. Each cord is provided with a pair of fastening means, one at either end of the ladder, to be linked with each other after the device has been wrapped about the tire.
This tire-slip preventing device has numerous advantages over the old tire chain made of metal. It is light, easy to carry and rust proof. Furthermore, it has the merit of causing much less damage to both the tire on which it is used and the road surface over which the vehicle travels. Nevertheless, it has an important drawback in that it is difficult to fit tightly on the tire.
The device is designed to fit snugly on a tire T in the ideal state depicted in FIG. 2. That is, the length of the cross belts (the width of the device), their spacing on the cords and the position of the fastening means are selected so that when the cords are drawn fully taut, they will draw the projecting ends of the cross belts down onto the side walls of the tire in a state where the cross belts are evenly spaced about the tire surface. In actual use, however, it is extremely difficult to attach the device to a tire in this state, particularly if the tire is attached to a vehicle which prevents access to inward side of the tire. When the device is wrapped about the tire, the ends of the cross belts 2 tend to stick out to the sides because of their resilience as shown in FIG. 3. Theoretically, it is possible to make these protruding ends bend toward and lie flat on the side walls of the tire by shortening the effective length of the cords 1a and 1b. This requires an impractically large force, however, since it is necessary to overcome not only the resilient force of the cross belts but also the force of friction between the cross belts and the face of the tire and this latter force becomes progressively larger as the tightening operation proceeds. A person attaching the device by hand may not experience any severe difficulty in wrapping the ladder about the tire and linking the connecting metals 4 to obtain the degree of fit shown in FIG. 3. However, he will find it virtually impossible to attain the degree of fit shown in FIG. 2 merely by pulling at the opposite ends of the cords 1a and 1b. Consequently, although the conventional antislip device of this type works very well when attached to the tire in the ideal state, such a great amount of strength is required to attain this state that the device is in fact almost always used with cross belts spaced at somewhat irregular intervals and projecting from the edges of the tire. Furthermore, the conventional tire-slip preventing device can be attached to the tire only by raising the tire off the ground or by driving the tire of the vehicle onto the device.